1. Field of the Invention
The present invention relates to a copy protection system and method for optical disks, and a copy protected optical disk.
2. Description in of Related Art
Optical disks, such as compact disks, have been developed and produced since 1981. Because of their large memory capacity, the use of optical discs and their production has dramatically increased. Besides their large storage capacity, optical discs make it possible to copy information at relatively low cost while keeping signal quality substantially the same as the disk being copied.
It is now possible for almost anyone to manufacture optical discs easily due to the low-cost of production equipment. Unfortunately, it has also become easier to manufacture illegal copies of optical discs containing valuable software. This has resulted in great financial losses to the software industry. Illegal copying has also had detrimental effects on software development. Namely, companies are less willing to invest substantial time and money in the development of software.
Various techniques have been proposed to prevent illegal copying of optical disks. Examples of such techniques include the use of holograms placed on the optical disk, use of a serial number added to the software recorded on the disk, and the requirement that users enter an identification number or password to operate the software on a disk. However, these techniques have proved inefficient, and disadvantageously increase the cost of producing an optical disk.
The present invention relates to a method and apparatus for copy protecting an optical disk wherein test data, including modified first signals, is recorded on an optical disk such that, when reproduced, random ones of these modified first signals are reproduced as second signals. Both the first and second signals represent data having at least two zeros between successive ones.
The present invention further relates to a method and apparatus for optical disk authentication and reproduction. An optical disk is authenticated by creating a statistical version of the test data through repeated reproduction of the test data. If the test data matches references data, possibly recorded on the optical disk as well, the optical disk is authenticated. Once authenticated, reproduction of the optical disk is permitted. If the test data forms part of the data for reproduction, then the statistical data is output as the reproduced data.
The present invention further relates to an optical disk having been copy protected according to the present invention.